This invention relates generally to locomotives, and more specifically, to an apparatus and method for testing locomotive engines and associated systems.
During routine shop maintenance, generally every ninety-two days, the diesel engine of a locomotive is tested. For example, the diesel engine is typically operated at various predetermined horsepower levels while onboard temperature sensors and engine control parameters are recorded. The recorded data is then archived for future reference.
FIG. 1 diagrammatically illustrates a power plant system 10 of a locomotive. A diesel engine 30 is tested by operating throttle 20, which throttle 20 is operably connected to diesel engine 30, at each throttle position or notch. Each throttle position sets and fixes a different engine speed (i.e., rpm). A dynamic braking grid 50 (resistive heating elements used for braking the locomotive) imposes a load on an alternator 40, which alternator 40 is operably connected to diesel engine 30, to achieve a maximum horsepower for the set throttle position. During the test, electrical power normally provided to electric traction motors 60 for driving the wheels of the locomotive is diverted to dynamic braking grid 50. Each throttle position is maintained for a period of 15 to 20 minutes.
Attempts to analyze the recorded data are often unsuccessful because the water cooling radiator fans 80 of radiators 70 cycle between discrete speeds (off, 1/4 speed, 1/2 speed, full speed) while maintaining the cooling water at an operating temperature of, for example, 155 degrees F. In addition, changing of the radiator fan speed is accomplished by having radiator fans 80 brought up to full speed and then adjusted downwardly to the desired lower speed. Fluctuation in the water cooling temperature due to the cycling of radiator fans 80 ranges from 5 degrees F. to 10 degrees F. depending on the throttle position and the ambient air temperature. The transient nature of the cooling system precludes accurate diagnostics of diesel engine 30 and associated systems, for example, thermal diagnostics that are on the same order of magnitude as the fluctuation in temperature of the water for determining whether the cooling system is operating a few degrees too hot or too cold. For diesel engine 30 operating at, for example, 900 rpms and 3,300 hp, FIG. 2 illustrates a graph of the cyclic nature of the cooling water temperature over time.
The cycling of radiator fans 80 on and off also varies the load on diesel engine 30 so that the horsepower generated by the engine (as determined by measuring the current and voltage produced by the alternator) varies over time as illustrated in FIG. 2. In particular, radiator fans 80 have a diameter of three to four feet and draw 100 hp during operation.
While such a test may indicate whether engine 30 is operating generally at an expected horsepower level at a specific throttle position, such a test cannot be used to readily identify trends in the performance of the engine, the thermal systems, the electrical power systems, etc. For example, on a hot day, although the horsepower level of the engine may be reached, the radiator fans may be operating at 3/4 speed when they should be operating on 1/2 speed, or the fuel system may be providing excess fuel to the engine in order to reach the desired horsepower level.
Therefore, there is a need for an apparatus and method for testing a power plant system of a locomotive in which engine and associated systems are maintained in a thermally steady state.